Our third death marker is Brain Natriuretic Peptide, a relatively small protein secreted by human heart muscle cells. It is NOT made in the brain in humans, but is named Brain Natriuretic Peptide because it was originally identified in pig brains. Go figure! At any rate its major actions in the body is to decrease the resistance to blood flow by blood vessels and to make you pee out more sodium, which is where the natriuretic in its name originates. The Latin name for the element sodium is natrium and the chemical symbol for sodium is Na. Brain Natriuretic Peptide is commonly identified by the abbreviation BNP. There are standard lab tests to measure it in the blood. A precursor to BNP, called NTpro-BNP can also be measured in the blood. Both tests give essentially the same information but they cannot be used interchangeably because the reference (normal) ranges are not the same, something a lot of primary care providers don’t seem to get. In this post I use BNP for both BNP and NTpro-BNP. BNP was originally identified as a marker for acute heart failure and is a useful test in the ER for that condition. BNP is also quite useful as a prognostic test in patients with known heart failure. So the level of BNP in the blood correlates with how well a heart failure patient will do in the future. But what I am interested in is that BNP is a useful predictor of overall mortality (that is, death). Let’s look at 3 levels of BNP and how it relates to death (data is from reference 1).

This increased death rate in people with BNP levels in the highest third (green in the above graph) correlates strongly with people experiencing heart failure, as shown in the following graph:

So why is BNP such a nice predictor of death? Because it measures how much heart muscle cells are being stretched, which is something these types of muscle cells don’t like, probably because it increases the amount of work of contracting the cell, which is what happens when your heart “beats.” Indeed, this association of BNP with heart muscle contraction has been directly linked to the electrical activity of the heart, the standard measurement of which is called the EKG. The figure below illustrates the portions of the EKG. The part of the EKG that directly correlates with the BNP is the QT interval.